Attribution matters here because whoever's officially credited gets their estate, heirs, or institution claiming rights to reproduction, licensing, and control over how the work's presented to the world - that's real money when you're talking about one of Europe's most photographed ceilings. The court case is basically asking: if Lenepveu did the original design and Chagall painted over it in the 1960s, is it Chagall's work, Lenepveu's, or a collaboration? and who gets to say what happens to it next.
If you actually want to see what the dispute is about instead of just reading legal summaries, look for side-by-side comparisons of the original Lenepveu sketches versus photos of what's up there now - seeing the actual visual differences makes it way clearer why historians are split, and that's usually more useful than whatever the court decides anyway.